they actually explained the fight in the LA Daily News yesterday.
Seems there's a local barber who cuts the hair for many of the USC players including both Hackett and Lewis. For some reason, hackett blamed the barber for the recent ESPN Outside the Lines story that featured Hackett and his dad as an obvious package deal(and pointed out the NCAA did NOT know Hackett wasn't on scholarship but got free tuition as the son of a USC employee).
So after the game Hackett went after the barber who was in the crowd at the game. Lewis defended the barber, the fight ensued. hackett was apparently so furious he came out again after everything had died down, and had to be restrained by security again.
USC has had no official comment and according to Daily News writer Scott Wolf no suspensions are other disciplinary action is expected, Floyd considers it just a normal thing that happens, just happened to be seen by the public this time.